The objective is to complete animal and clinical testing of a catheter tip device which measures instantaneous blood flow in the pulmonary artery or the aorta. The principle of operation is based upon ultrasonic detection of blood velocity and vessel cross-section area. The product of these gives instantaneous volume flow. The validity of the measurement technique has been demonstrated in earlier work in dogs using manual data collection and off-line processing. A high correlation (.99) was found between cardiac output measurements made using botht eh ultrasonic method and the dye indicator-dilution method. An automated data collection and processing system which provides continuous measurements, stroke volume and cardiac output of cardiac blood flow and beat-per-beat measurement has not been completed. Initial on-line measurements with it in dogs, have demonstrated high potential for its use in providing crucial therapeutic guidance information in managing critically ill and major surgery patients. For example, immediate cardiac flow response to drug and anesthetic applications, PEEP and fluid infusion have been measured with it. We wish to accomplish several specific objectives: 1) complete testing of the system with dogs to document its accuracy, dynamic response and safety; 2) evaluate its potential utility in animals under conditions similar to clinical situations; 3) complete refinements to the catheter and electronic system; and 4) evaluate the unit in a number of clinical situations. Objectives of the clinical evaluation will be initially to verify the unit's performance in humans, and then to assess its utility in diverse clinical situations, such as in the Operating Room and Intensive Care Unit.